Endless belt printing machine



July 7, 1970 E. A. STROUD ET L ENDLESS BELT PRINTING MACHINE 3 Sheets-Sheet 1 Filed June 30, 1967 @m &

Mm m w W N mmo flfl o M TSA S N .A Y EA E V S N DE R m A T WH MW, A EC July 7, 1970 E. A. STROUD ET AL ENDLESS BELT PRINTING MACHINE 3 Sheets-Sheet 2 Filed June 30, 1967 y 7, 1970 I E. A. STROUD ET AL 3,518,940

ENDLESS BELT PRINTING MACHINE Filed Julie 30, 1967 3 Sheets-Sheet 5 United States Patent ENDLESS BELT PRINTING MACHINE Edward A. Stroud, Wharton, and Charles Aaron, West Caldwell, N.J., assignors to Cameron Machine Company, Dover, N.J., a corporation of New York Filed June 30, 1967, Ser. No. 650,338 Int. Cl. 341i /04, 13/02 US. Cl. 101-223 Claims ABSTRACT OF THE DISCLOSURE The apparatus of this invention embodies a printing mechanism comprising an endless belt formed of polyethylene terephthalate and carried by an idler roll and a plate cylinder, a drive engaging the belt, the plate cylinder being free wheeling relative to the drive during normal high speed operation to permit independent belt travel over the free wheeling plate cylinder, and an adjustable tensioning assembly for selectively positioning the idler roll relative to the plate cylinder and tensioning the endless belt irrespective of its length.

This invention generally relates to automatic printing machines and more particularly to apparatus of a type incorporating a printing mechanism having an ordered arrangement of plates for printing a series of impressions on a web in proper sequence for effecting continuous printing of books, brochures and similar articles.

A principal object of this invention is to provide an improved printing machine particularly suited for ex tremely high speed operation.

Another object of this invention is to provide such a machine having a printing mechanism incorporating a new and improved printing band.

A further object of this invention is to provide an improved high production printing mechanism capable of quality printing in an automatic operation while effectively controlling dynamic inertia of a series of printing plates, mounted on a continuously traveling printing band, against surface walking and excessive multiplication of error.

Still another object of this invention is to provide an improved printing mechanism facilitating quick and easy set-up and disassembly, e.g., for printing books of different size while readily providing for corresponding adjustment and proper tensioning of a printing band.

Other objects will be in part obvious and in part pointed out more in detail hereinafter.

The invention accordingly consists in the features of construction, combination of elements and arrangement of parts which will be exemplified in the construction hereafter set forth and the scope of the application which will be indicated in the appended claims.

In the drawings:

FIG. 1 is an isometric view, partly broken away, schematically showing a printing machine incorporating this invention;

FIG. 2 is an enlarged diagrammatic side elevational view of a printing mechanism incorporated in the printing machine of FIG. 1;

FIG. 3 is an enlarged view, partly in section and partly broken away, taken generally along line 3-3 of FIG. 1;

FIG. 4 is an enlarged fragmentary view, partly in section and partly broken away, of apreferred mounting arrangement for a plate cylinder and an impression cylinder and showing a drive sprocket wheel associated with the plate cylinder;

FIG. 5 is an enlarged view, partly in section and partly broken away, taken generally along line 5-5 of FIG. 2;

FIG. 6 is a section view, partly broken away, taken generally along line 6-6 of FIG. 5;

FIG. 7 is a section view, partly broken away, taken generally along line 77 of FIG. 5; and

FIG. 8 is a diagram of an electrical circuit for an automatic tensioning assembly of this invention.

With reference to FIG. 1, a typical printing machine 10 incorporating a preferred embodiment of this inven tion is shown wherein a roll 12 of paper sheet material is mounted on an unwind assembly 14 having an associated tension control 16. A paper web 18 is fed along a path defined by a multiplicity of guide and transport rolls schematically shown in the drawing. It will be understood that the illustrated guide and transport rolls are rotatably mounted on a frame (which is not shown in FIG. 1 for clarity of illustration) and that suitable interconnected drive gear components are provided in the machine 10 for driving the various rolls such as at 20 under the power of an electric motor 22 in accordance with well known conventional techniques.

The web 18 passes over an impression cylinder 24 to engage an endless printing band 26 of a printing mechanism 28 after the printing band 26 has been inked by an inker 30 whereby the web 18 is printed on one side and then fed through an ink dryer 32. After being drawn over a pair of chill rolls 34, the web 18 passes over turning bars 36, 38 and a second impression cylinder 40 to present the other side of the web 18 to be printed by a second printing mechanism 42 whereupon the web 18 is pulled through a second dryer 44 and over a second pair of chill rolls 46 and is then drawn downwardly over an idler roll 48 by a driven roll 50 and fed to a slitting mandrel 52 which cuts the web 18 lengthwise into individual ribbons 54 of equal width. The ribbons 54 are each fed to a separate pair of folding cylinders such as at 56 and are delivered in stacked folded strips shown at 58 by a power driven nip feed roll 60 to a cutter mechanism 62, it being understood that suitable compensating rolls such as at 64 are provided to ensure proper registration of the stacked strips 58 being fed into the cutter mechanism 62. The latter comprises a stationary bed knife 66 which cooperates with a powered rotary multi-knife cutter 68 synchronized with the nip feed roll 60 to sever the stacked strips 58 into stacked sheets 70 of equal length which are then delivered by a high speed conveyor 72 to be collated, e.g., and bound into books.

With reference once again to the printing mechanisms 28 and 42, only printing mechanism 42 will be described in detail since each printing mechanism is of substantially the same construction.

Below the impression cylinder 40' is a plate cylinder (best seen in FIG. 2) which together with a plurality of spaced parallel idler rolls 82, 84, 86 support an endless printing band 88 for continuous movement along a path in one direction past inker 90 prior to engaging the portion of web 18 traveling over the impression cylinder 40.

As clearly shown in FIG. 3, the endless printing band 88 comprises an outer layer of flexible printing plates 92 attached to a backing layer or endless belt 94 of perforated construction wherein a row of holes 96 are punched along the length of the belt 42 adjacent each of its side edges for engaging a pair of sprocket wheels (only one shown at 100) coaxially mounted at opposite ends of the plate cylinder 80.

More specifically, the endless belt 94 is formed of linear polyester sheet material, preferably polyethylene terephthalate commercially available as Mylar, a tough self supporting, flexible solid sheet of, say, about 10 mils thick ness which is preferably oriented in both crosswise and oriented sheet exhibits substantially the same physical properties such as high tensile and tear strength over a wide range of temperatures and humidities and good elon gation and high impact resistance as measured in both crosswise and lengthwise directions. In addition to being dimensionally stable, the resulting belt material is also chemically resistant and stands up well under exposure to oils, greases, printing inks etc. providing a rugged durable belt 94 particularly suited for use in a printing mechanism.

The flexible printing plates 92 are preferably formed of rubber and are bonded to the belt 94 by a suitable laminating adhesive compatible with the polyethylene terephthalate belt material. The plates 92 each present raised impression surfaces for printing an individual page and are suitably arranged to print an ordered series of impressions on the web 18. The total number of printing plates 92 corresponds to the total number of pages in the book to be printed such that for a particular printing job the printing band 88 has a predetermined fixed length.

Such construction provides the further advantage of minimal belt thickness whereby the printing band 88 is usable even with a plate cylinder 80 of about eight inch diameter effecting a small bend radius for a precision high quality printing operation. Moreover, the above described perforated construction of the belt 94 facilitates assembly for a particular printing job in that the plates 92 are quickly and easily lined up in relation to the sprocket holes 96 adjacent opposite side edges of the belt 94.

The belt 94 exhibits a certain, albeit limited, degree of resiliency providing residual memory stresses to automatically return the belt to its original shape as the belt 94 is stretched in incremental steps under running tension applied by the sprocket wheels 100 upon passing over the plate cylinder 80, thereby effectively resisting elongation of the sprocket holes 96 even at high operating speeds in the order of 1,000 feet per minute.

In the prior art, printing machines have employed a series of printing plate carriers interconnected by hinge pins supported on chains engaging a sprocket integrally fixed on a plate cylinder member for driving it in unison with the chains driving the carriers. While such apparatus operate satisfactorily at relatively slow speeds, variable slippage occurs between the plate cylinder and inner sur faces of the carriers along a line of printing contact with the Web such that at high operating speeds excessive ac cumulation of error occurs and severe tensioning stresses develop in the material of the carriers, causing surface walking of the printing plates, bowing of hinge pins and even destruction of the hinge connections between carriers.

The present invention overcomes such objectionable difficulties by a free wheeling mounting of the plate cylinder 80 providing for the belt 94 to travel directly under the influence of the sprocket wheels 100 and independently of the plate cylinder 80 with minimal but continuously uniform relative slippage. The belt 94 is of greater width than the plate cylinder 80, and only unsupported opposite side edges of the belt are drivingly engaged. Such an arrangement ensures that the inner surface of the belt 94, in contact with the plate cylinder 80 and supporting the printing plates 92, is uniformly and longitudinally tensioned such that the faces of the printing plates 92 travel at an instantaneously uniform surface speed across the free wheeling plate cylinder 80 along a line of printing contact with the web passing over the impression cylinder 40, for trouble-free precision web printing at significantly increased speeds.

A preferred end mounting arrangement for the impression cylinder 40 and the plate cylinder 80 is illustrated in FIG. 4, opposite ends of these cylinders being mounted in an identical manner. The plate cylinder 80 and the impression cylinder 40 are each provided integral journals 102 and 104 supported for rotation in commercially available rnulti-row tapered roller bearing assemblies 106 and 108 suitably mounted in a well known manner in fixed relation to a frame for taking up both radial and axial thrusts applied to the cylinders.

In the illustrated embodiment, an eccentric sleeve 112 is shown providing radial support for the impression cylinder bearing assembly 108, and it will be understood that suitable provision is made for selectively rotating the eccentric sleeve 112 and locking it in a preselected position whereby the impression cylinder 40 can be operatively engaged and disengaged relative to the plate cylinder 80, as desired.

A drive hub 114 is rotatably supported on a pair of suitably confined, axially spaced ball bearing assemblies 116 and 118 carried on bearing surfaces 120 and 122 of plate cylinder 80 while inner and outer axial ends of the drive hub 114 respectively carry the sprocket wheel 100 and a spur gear 124 coaxially secured by suitable fasteners such as at 126 and 128. The sprocket wheel 100 has a series of circumferentially spaced sprockets such as at 130 registrable with the aforementioned sprocket holes 96 formed in the endless belt 94, and to preserve the integrity of the belt, the sprockets 130 are each rounded to remove any jagged edges or sharp corners. Spur gear rotation is effected by a common variable speed drive (not shown) or by any other type of driving arrangement in synchronism with the main drive of the machine, and the sprocket wheels 100 will be seen to be mounted for rotation independently of the free wheeling plate cylinder 80 for driving the printing band 88 over the same in synchronized relation to the passage of the web 18 over the impression cylinder 40.

So that the printing band 88 can be accelerated and decelerated between a rest condition and a desired operating speed in precisely timed relation to the passage of the web 18 without applying excessive force to portions of belt 94 surrounding the sprocket holes 96, a friction clutch 132 is preferably provided between the sprocket wheels 100 and the free wheeling plate cylinder 80.

Specifically, a clutch ring 134 is shown slidably mounted on a plurality of circumferentially spaced pins (only one shown at 136) pressed fit to the drive hub 114 and axially extending through the sprocket wheel 100 such that the clutch ring 134 is rotata-bly coupled to the drive hub 114 while being free to slide relative thereto in an axial direction. A disk or clutch lining 138 of suitable friction material is firmly fixed to an inner face of the clutch ring 134 for engaging a clutch face 140 of a circular plate 142 concentrically secured by a screw 144 to a shoulder 146 of the plate cylinder 80.

To vary the effective range of the friction clutch 132 coupling the sprocket wheels 100 to the plate cylinder 80, a plurality of equiangularly spaced compartments (only one shown at 148) are formed to extend axially through the sprocket wheel 100 and into adjoining portions of the drive hub 114 and clutch ring 134. A coil compression spring 150 is fitted within each compartment 148 with one end of the spring 150 seated against the clutch ring 134 and its opposite end engaging an enlarged head 152 of an adjusting screw 154 extending axially through a tapped hole in the drive hub 114 and in threaded connection to a lock nut 156 drawn up tightly against the same for maintaining an adjusted degree of spring compression.

The eifective limit of the friction clutch 132 in trans mitting torque to the plate cylinder 80 thus can be readily preset at a sufliciently high level to effect proper acceleration and deceleration of the printing band 88 while yet ensuring independent travel of the belt 94 in uniform relation to the free wheeling plate cylinder 80 as described above for effecting precision operation at extremely high speeds.

While satisfactory results may be obtained without malfunction through a wide range of operating speeds in using impression cylinder 40 as an idler, a driven gear, such as that shown in broken lines at 158, may be coaxially fixed on the impression cylinder 40 to mesh with the spur gear 124 of the plate cylinder 80. Such an arrangement ensures proper synchronism of the impression cylinder 40 and minimizes any tendency of snapping the web 18 during relatively rapid accelerations and decelerations of the machine 10.

To readily modify machine 10 in minimal time for printing different size books, a printing band tensioning assembly 160 (FIGS. -7) is incorporated in this invention for selectively tensioning printing bands of varying length corresponding to different size books.

The printing band 88 of preselected length is trained over plate cylinder 80 and idler roll 82 to be automatically tensioned by controlled movement of the idler roll 82 relative to the free wheeling plate cylinder 80. As best seen in FIG. 2, intermediate idler rolls 84, 86 are provisionally provided in the event the length of the printing band 88 is sufiicient to warrant intermediate support, and while not illustrated, it will be understood that these additional idler rolls are suitably journalled in the machine frame.

The idler roll 82 is shown as being of tubular construction and suitably supported for rotation on a horizontally disposed support shaft 162 having yokes 164 and 166 fixed at its opposite ends and secured to traversing carriers 168 and 170 for movement above vertical pivot axes. Rollers such as at 172 support thetraversiug carriers 168, 170 for smooth and easy rolling movement along horizontal guide rails 174, 176 of the machine frame, and a pair of lead screws 178, 180 extend in adjacent parallel relation to the guide rails 174, 176 for imparting controlled movement to the traversing carriers168, 170.

Each lead screw 178, 180 is preferably mounted in a similar manner and it will be suflicient for a proper understanding of this invention to describe only one lead screw mounting. With reference to lead screw 178, its right hand end portion is mounted for rotation as well as for axial movement within a bearing housing such as at 18-2, and the left hand end portion of lead screw 178 is supported for rotation within a housing 186 suitably retained for simultaneous axial movement with the lead screw 178 to an extent limited by spaced stop plates 188, 190 fixed to a frame portion 192, the screw support housing 186 being shown supported on anti-friction ball bushings 194, 196 carried on fixed shafts 198, 200 secured to the stop plates 188, 190.

Each lead screw 178, 180 is in threaded engagement. with a traveling nut 202 (FIG. 6) loosely fitted within a pivot block 204, 205 mounted in each traversing carrier 168, 170. While being provided a preselected degree of radial clearance, each traveling nut 202 is firmly retained against axial movement relative to its respective traversing carrier.

To move the idler roll 82 toward and away from the plate cylinder 80, simultaneous rotation of the lead screws 178, 180 is effected by sprockets 206, 208 drivingly connected to lead screws 17 8, 180 and engaged with an endless drive chain 210 meshing with a sprocket 212 mounted on an output shaft 214 of a reversible electric motor 216.

As lead screw rotation is provided in a proper direction to move idler roll 82 to the left away from the plate cylinder 80 as seen in FIG. 2, one end of the idler r011 82 will normally engage in the printing band 88 before the other end since leads on both screws 178, 180 are unlikely to be exactly identical, and as one end of the idler roll 82 (adjacent traversing carrier 168, e.g.) begins to apply tension to the printing band 88, linear movement of the corresponding traveling nut 202 will stop together with traversing carrier 168, whereby continued rotation of lead screw 178 under the power of the motor 216 will move lead screw 178 axially to the right toward the plate cylinder 80.

Automatic control of the tensioning of printing band 88 is most clearly understood by referring to FIG. 6 wherein it is seen that a loading force exerted by the motor 216 to move the lead screw 178 axially to the right must be of suflicient magnitude to overcome a biasing force applied to the screw support housing 186 by a low friction diaphragm type fluid cylinder 218 via its reciprocable operating arm 220 and connecting link 222 pivotally mounted on frame portion 192.

As the screw support housing 186 moves slightly to the right away from its stop plate 188 against the force of the fluid cylinder 218 responsive to right hand axial movement of the lead screw 178, the traversing housing 168 remains substantially stationary relative to the frame by virtue of the described lead screw and traveling nut arrangement during continued rotation of the lead screws, and the other traversing carrier will continue advancing to the left until all slack has :been taken up in the printing band 88. Lead screw and its support housing 224 then will likewise be caused to shift axially against a cylinder load identical to that exerted on lead screw 178, it being understood that screw support housing 224 is also biased to the left in the same manner as screw support housing 186 under the force of a fluid cylinder of an area equal to that of third cylinder 218 with both fluid cylinders being connected to a common source of fluid pressure.

With both fluid cylinders applying an equal loading force to the housings 186, 224 upon their being shifted away from stop plates 188, the loading force is transmitted to the traversing carriers 168, 170 via lead screws 178, 180, and the printing band 88 will then be under uniform tension with the idler roll 82 automatically positioned parallel to the printing band 88.

As the screw support housings 186 and 224 continue to shift to the right, the resulting pivotal movement of links 222, 223 releases a pair of normally open microswitches 226, 227 connected in parallel circuit arrangement with the motor 216 (FIG. 8) to automatically open the circuit and de-energize the motor 216, it being understood that microswitches 226, 227 are closed by links 222, 223 when the latter are positioned in starting position against their left hand stop plates 188, 188.

With the motor stopped and a main switch 228 to the motor 216 being opened, the tensioned printing band 88 may then be adjusted by hand, if desired, by a pressure regulator 229 connected in the fluid circuit of the fluid cylinders 218 to ensure precision tensioning of the printing band for proper operation at the significantly increased operating speeds attainable in the printing mechanism of this invention.

Any tendency of the traversing carriers 168, 170 to become misaligned relative to their traveling nuts 202 or lead screws 178, 180, is effectively accommodated by the above described pivotal yoke mounting provided for the idler support shaft 162 and the preselected radial clearance between each traveling nut 202 and its respective pivot block 204, 205. Proper lateral positioning of the traversing carriers 168, 170 is assisted by the provision of two pair of side rollers 230, 232 on carrier 168 for engaging opposite sides of guide rail 174 and a single pair of side rollers 234 is mounted on the other carrier 170 engageable with guide rail 176 thereby to minimize any possibility of the tensioning assembly becoming wedged or binding against the rails 174, 176.

To provide a fail-safe arrangement wherein the established printing band tension will be maintained for proper operation even at speeds of about 1,000 f.p.m. despite a failure in fluid pressure, as well as to accommodate any backlash or lost movement due to manufacturing variations and tolerances in the component parts of the tensioning assembly 160, each traversing carrier 168, 170 is provided with suitable locking handle and shoe devices such as at 236 for clamping the traversing carriers 168, 170 to their respective guide rails 174, 176, and a clamping device 238 is desirably provided in the preferred embodiment for securing each locking handle to its traversing carrier. Thereafter, the fluid cylinders 218 can be deactivated with the tensioning assembly 160 conditioned for the printing operation.

rorn the foregoing description it is believed apparent that the machine of this invention provides for extremely high speed printing operation whereby malfunctions caused by surface walking of the printing plates are virtually eliminated in a printing mechanism exhibiting desirable flexibility for high quality printing of books of different size while yet requiring minimal time and effort in set-up and disassambly of different printing jobs.

As will be apparent to persons skilled in the art, various modifications, adaptations and variations of the foregoing specific disclosure can be made without departing from the teachings of the present invention.

We claim:

1. In a high speed printing machine having a frame, an impression cylinder journalled on the frame and feeding means for passing a web over the impression cylinder, a printing mechanism comprising an endless belt, a plurality of flexible printing plates carried on an outer surface of the endless belt, a plurality of rotary supports mounted on the frame and supporting the endless belt for continuous travel along a path in one direction, the rotary supports including a free wheeling plate cylinder journalled on the frame in adjacent parallel relation to the impression cylinder, and positive drive means for driving the endless belt independently of the free wheeling plate cylinder, the positive drive means engaging a portion of the endless belt traveling past a line of printing contact with the web passing over the impression cylinder to effect a uniform longitudinal tension on an inner surface of the belt in contact with the plate cylinder such that the faces of the printing plates travel at an instantaneously uniform surface speed across the free wheeling plate cylinder along said line of printing contact.

2. The mechanism of claim 1 wherein the endless belt is formed of a flexible, tough, impact resistant, synthetic sheet exhibiting high tensile strength and dimensional stability in a high speed operation.

3. The mechanism of claim 1 further including an adjustable tensioning assembly having a pair of traversing carriers movably mounted on the frame and supporting one of the rotary supports in selectively adjusted positions relative to the free wheeling plate cylinder to accommodate varying lengths of the endless belt.

4. The mechanism of claim 3 wherein the tensioning assembly further includes a power actuated automatic tensioning control for moving said one rotary support into direct engagement with the endless belt to establish a uniform longitudinal tensioning force thereon.

5. In a high speed printing machine have a frame, a printing mechanism comprising an endless belt having a row of perforations formed adjacent each side edge thereof, a plurality of flexible printing plates carried on an outer surface of the endless belt intermediate the rows of perforations, a plurality of rotary supports including a free wheeling plate cylinder journalled on the frame and supporting the endless belt for continuous travel along a path in one direction, the endless belt being a greater width than the plate cylinder to effect continuous running engagement therewith between the rows of perforations, and sprocket drive means mounted coaxially of the plate cylinder for operation independently thereof and registrable with the perforations of the endless belt for driving the same.

6. The mechanism of claim 5 wherein the endless belt is formed of polyethylene terephthalate sheet material.

7. In a high speed printing machine having a frame, a plate cylinder and an idler roll mounted in parallel relation on the frame for supporting an endless printing band for unidirectional movement along a path, an automatic printing band tensioning assembly comprising a pair of traversing carriers supporting opposite ends of the idler roll and mounted on the frame for movement toward and away from the plate cylinder, a pair of driven lead screws journalled on the frame for both rotary movement and axial movement toward and away from the plate cylinder, the lead screws each being threadably connected to one of the traversing carriers for moving the idler roll away from the plate cylinder to an extent limited by the length of the endless printing band, and a tensioning control for applying equal loading forces against axial movement of the lead screws toward the plate cylinder when the ends of the idler roll are stopped, thereby to establish a uniform longitudinal tensioning force on the printing band.

8. In a high speed printing machine having a frame, an impression cylinder journalled on the frame and feeding means for passing a web over the impression cylinder, a printing mechanism comprising an endless belt, a plurality of flexible printing plates carried on an outer surface of the endless belt, a plurality of rotary supports mounted on the frame and supporting the endless belt for continuous travel along a path in one direction, the rotary supports including a free wheeling plate cylinder journalled on the frame in adjacent parallel relation to the impression cylinder, positive drive means engaging the endless belt for driving the same independently of the free wheeling plate cylinder, the positive drive means being supported in concentric relation to the axis of the plate cylinder to effect a uniform longitudinal tension on an inner surface of the belt in contact with the plate cylinder such that the faces of the printing plates travel at an instantaneously uniform surface speed across the free wheeling plate cylinder along a line of printing contact with the web passing over the impression cylinder, an inker mounted on the frame for transferring ink to the printing plates upstream of their engagement with the web, and an adjustable tensioning assembly having a pair of traversing carriers movably mounted on the frame and supporting one of the rotary supports in selectively adjusted positions relative to the free wheeling plate cylinder to accommodate endless belts of varying lengths.

9. The mechanism of claim 8 further including a power actuated tensioning control including a pair of lead screws mounted on the frame, the lead screws each being threadably connected to one of the traversing carriers for moving said one rotary support relative to the free wheeling plate cylinder to establish a uniform longitudinal tension force on the endless belt.

10. The mechanism of claim 8 wherein the endless belt is formed of a polyethylene terephthalate strip of sheet material.

11. In a high speed printing machine having a frame, an impression cylinder journalled on the frame and feeding means for passing a web over the impression cylinder, a printing mechanism comprising an endless belt of perforated construction having a row of holes formed adjacent each side edge thereof, a plurality of flexible printing plates carried on an outer surface of the endless belt, a plurality of rotary supports mounted on the frame and supporting the endless belt for continuous travel along a path in one direction, the rotary supports including a free wheeling plate cylinder journalled on the frame in adjacent parallel relation to the impression cylinder, and a pair of driven sprocket wheels supported at opposite axial ends of one of the rotary supports for rotation independently thereof, the sprocket wheels being registrable with the holes of the endless belt for driving the same independently of the free wheeling plate cylinder to effect a uniform longitudinal tension on an inner surface of the belt in contact with the plate cylinder such that the faces of the printing plates travel at an instantaneously uniform surface speed across the free wheeling plate cylinder along a line of printing contact with the web passing over the impression cylinder.

12. The mechanism of claim 11 wherein the sprocket wheels are each provided with rounded cogs for preserving the integrity of the endless belt.

13. The mechanism of claim 11 wherein the pair of sprocket wheels are supported at opposite ends of the free wheeling plate cylinder, and wherein a driving connection is provided between the free wheeling plate cylinder and the pair of sprocket wheels, the driving connection including torque transmitting means selectively operable to maintain the endless belt against slippage relative to the free Wheeling plate cylinder during acceleration and deceleration of the sprocket wheels.

14. The mechanism of claim 13 wherein the torque transmitting means comprises a friction clutch with biasing means for imparting a resilient frictional force to the free wheeling plate cylinder in response to rotation of the sprocket wheels between a rest position and a preselectable angular speed thereof, the biasing means being settable for selectively varying the effective range of the friction clutch such that an increase in speed of the sprocket wheels beyond said preselectable angular speed overcomes the resilient frictional force of the biasing means and causes slippage of the friction clutch to permit the endless belt to be driven over the free wheeling plate cylinder at a uniform surface velocity independently of the free wheeling plate cylinder.

15. In a high speed printing machine having a frame, a plate cylinder and an idler roll mounted in parallel relation on the frame for supporting an endless printing band for unidirectional movement along a path, an automatic printing band tensioning assembly comprising a pair of traversing carriers supporting opposite ends of the idler roll and mounted on the frame for movement toward and away from the plate cylinder, a pair of driven lead screws journalled on the frame for both rotary movement and axial movement toward and away from the plate cylinder, a pair of screw support housings mounted on the frame for rotatably supporting the lead screws, the screw support housings each being retained on their respective lead screw for simultaneous linear movement therewith, the lead screws each being threadably connected to one of the traversing carriers for moving the idler roll away from the plate cylinder to an extent limited by the length of the endless printing band, and a tensioning control operable on each of the lead screws to selectively balance opposite ends of the idler roll in pressing engagement against the endless printing band, the tensioning control including biasing means operable on each of the screw support housings for applying equal biasing forces thereto in opposition to linear movement toward the plate cylinder upon its corresponding traversing carrier being stopped by engagement of the idler roll with the printing belt for effecting equal tensioning loading forces on the printing band.

16. The assembly of claim 15 wherein the biasing means comprises a pair of fluid cylinders connected to a common source of the fluid pressure, the fluid cylinders each having an extendible and retractable operating member connected to one of the screw support housings for applying equal biasing forces thereto.

17. The assembly of claim 16 further including motor drive means for simultaneously driving the lead screws, and limit switch means connected to the motor drive means for de-energizing the same in response to movement of both operating members upon each of the screw support housings moving a preselected distance under equal tensioning loading forces in opposition to biasing forces of equal magnitude applied thereto by the operating members.

18. The assembly of claim 16 further including locking means for securing each of the traversing carriers to the frame upon establishing a uniform longitudinal tensioning force on the endless printing band and deactivating the fiuid cylinders to provide fail-safe operation of the printing machine.

19. In a high speed printing machine having a frame, an impression cylinder journalled on the frame and feed- 1 ing means for passing a web over the impression cylinder, a printing mechanism comprising an endless belt, a plurality of flexible printing plates carried on an outer surface of the endless belt, a plurality of rotary supports mounted on the frame and supporting the endless belt for continuous travel along a path in one direction, the rotary supports including a free wheeling plate cylinder journalled on the frame in adjacent parallel relation to the impression cylinder, a positive drive means engaging the endless belt for driving the :same independently of the free wheeling plate cylinder to effect a uniform longitudinal tension on an inner surface of the belt in contact with the plate cylinder such that the faces of the printing plates travel at an instantaneously uniform surface speed across the free wheeling plate cylinder along a line of printing contact with the web passing over the impression cylinder, torque transmitting means between the free wheeling plate cylinder and the positive drive means, the torque transmitting means being selectively operable to maintain the endless belt against slippage relative to the free wheeling plate cylinder during acceleration and deceleration of the drive means, an inker mounted on the frame for transferring ink to the printing plates upstream of their engagement with the web, and an adjustable tensioning assembly having a pair of traversing carriers movably mounted on the frame and supporting one of the rotary supports in selectively adjusted positions relative to the free wheeling plate cylinder to accommodate endless belts of varying lengths.

20. In a high speed printing machine having a frame, a printing mechanism comprising a belt, a plurality of flexible printing plates carried on the belt, a plurality of rotary supports including a free wheeling plate cylinder journalled on the frame and supporting the belt for continuous travel over a path in one direction, positive drive means engaging the belt for driving it independently of the free wheeling cylinder, and torque transmitting means between the positive drive means and the free wheeling plate cylinder, the torque transmitting means being selectively operable to maintain the belt against slippage relative to the free wheeling plate cylinder during acceleration and deceleration of the positive drive means.

References Cited UNITED STATES PATENTS 2,128,343 8/1938 Bemis et a1. 101-178 2,788,738 4/1957 Wood 101-180XR 2,836,528 5/1958 Ford 161-231 XR 2,938,823 5/1960 Salem et al 161-231 XR 3,141,405 7/1964 Tombeur 101-378 3,329,088 7/ 1967 Rockefeller 101-426 FOREIGN PATENTS 574,608 3/ 1958 Italy.

ROBERT E. PULFREY, Primary Examiner J. R. FISHER, Assistant Examiner US. Cl. X.R. 

